Sticking half-bridge smps FETs together with what?

[grizedale]

Hello,

I do half-bridge smps converter for audio power supply.

No heatsink is required as average power much less then peak power.

However, the FETs will get hot, so i want them both to be the same temperature as each other.
-Otherwise i may get unequal currents as each fet conducts, due to rds(on) differences.

Anyway, i will put the fets back to back , and stick them together with that sticky white stuff which sets like hard rubber.

But i cant remember the name of the sticky white stuff.

Do you know what it is?

 

[technoqwerty123]

Hello,
I think you are refering to RTV (room temperature vulcanization) Silicone. Checkout

Regards

 

[alexan_e]

I assume that you mean the thermal grease Thermal grease - Wikipedia, the free encyclopedia
and you will probably need to use an insulating pad between them too (depending on the case)

Alex

 

[mtwieg]

I was thinking thermal grease at first, but as far as I know thermal grease doesn't cure and become hard (at least it's not supposed to). Most thermal paste isn't "sticky" at all. Just oily.

 

[alexan_e]

I assume that he only needs the grease for thermal conductivity, if he needs a glue like substance then there are thermally conductive adhesives or silicones.

Alex

 

[grizedale]

Hi,

It is indeed the RTV type stuff that im after, tanks very much for that technoqwerty........which is nicely thermal conducting and sets hard.

The FETS are STP11NK40ZFP, and these have insulated tabs so need no insulation pads or anything like that......

STP11NK40ZFP
https://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00003028.pdf


In fact, i cannot work out why anyone would want to use a TO220 FET with a metal tab any more?.......whats the point in having your heatsink electrically connmected to your drain.....spraying emissione everywhere?

The insulated tab TO220's have about the same thermal resistance too...so its not as if your going to run much cooler with a metal tab to220 fet.

 

[Raza]

Hi grizedale,
Here is the part number what you need.
1-Part Adhesive Sealant TSE3941
It perfectly fits your need and you can order @

Hope it helps you. Good Luck.